U.S. Pat. No. 6,247,489 to Maskell, et al., discloses an exemplary check valve especially useful as part of the water-recirculation system of a swimming pool, spa, or hot tub. The check valve includes a housing and a cover removably attached thereto. The housing may include coupling portions defining ports through which fluid may enter and exit the housing.
Pivotally attached to the cover of the check valve of the Maskell patent is a flapper assembly. The flapper assembly may comprise a diverter member having a body and two attachment arms. Pins are inserted through bores in the arms and the cover to attach the diverter member of the flapper assembly to the cover.
A spring (or other biasing member) may be positioned between the cover and the flapper assembly of the valve of the Maskell patent. The spring functions to bias the flapper assembly “into sealing engagement” with seats associated with the housing. Hence, when fluid flows through a conduit and into the entry port of the valve,                it contacts the flapper assembly and pivots it to an open position . . . wherein fluid is permitted to enter the central area of the valve and exit through the [exit] port. However, should the fluid . . . be discontinued or otherwise attempt to flow out from the central area through the [entry] port, the flapper assembly is pivoted by virtue of contact with such fluid and by the biasing force of the spring [which] serves to bias [the flapper assembly] into contact with the seat to achieve a fluid-tight seal therebetween.The contents of the Maskell patent are incorporated herein in their entirety by this reference.        